In the production of metal strip, e.g. steel strip by the hot rolling of slabs in a hot-rolling line, the strip which is fabricated may be coiled on a mandrel to form a strip coil or reel in a conventional band or strip coiler located beneath the floor of the strip mill.
Such strip coilers are referred to as subfloor coilers and comprise, in addition to the mandrel, a plurality of guide or pressing elements which are disposed in angularly spaced relationship about this mandrel and serve to press the oncoming strip thereagainst and against previously wound turns, or to guide the strip onto the mandrel or onto the previously formed turns.
Such guide or pressing means can include pressing rollers or rolls which are rotatable about axes parallel to the mandrel axis. The guide or deflecting plates may be in the form of arcuate shells which extend along a portion of the arc of the coil and can define a narrow gap therewith so that they can serve to deflect the strip onto the coil or the mandrel.
It is common to provide such guide or pressing elements, or both, upon an assembly which is capable of adjusting the position between the mandrel surface and the pressing or guide element, i.e. the roll or plate.
Such an assembly can comprise a so-called four-pivot linkage having at least two arms, each of which is pivotally connected at one end to a head carrying the pressing or guide element.
The other ends of these arms are pivoted as well so that the pivots and the two arms form the vertices and two sides of a quadrilateral and any displacement of the linkage results in a displacement of the pressing roll or guide plate generally parallel to itself toward or away from the mandrel.
This linkage can be actuated by a combined pneumatic hydraulic unit which serves for closing and opening the pressing roll assembly with respect to the coiling mandrel.
Subfloor strip coilers for hot-rolling strip mills have generally comprised in the past a large volume pneumatic cylinder which serves to position the pressing rollers, i.e. moving them toward and away from the mandrel and correspondingly displacing any deflecting or guide shell.
Such large volume pneumatic cylinders have been found to be disadvantageous in practice when the pressing roll or guide shell is to be swung toward or away from the mandrel.
As is described in Technical Review, February 1978, Mitsubishi Heavy Industries, Ltd., pages 1-10, a hydraulic shock absorber can be combined with a pneumatic cylinder for the pressing rolls or guide shells of subfloor strip coilers.
Such hydraulic shock absorbers differ from conventional hydraulic cylinders in that the piston rod of the shock absorber contains a piston-forming pressure accumulator. The latter accumulator has on one side compressed nitrogen gas while on the other side a hydraulic pressure is developed by a working piston displaceable in the hydraulic cylinder. By pressurization of the piston shiftable in this cylinder with fluid under pressure, the piston rod is brought into a position in which the pressure of the nitrogen gas is in equilibrium with the hydraulic pressure. The use of such a hydraulic shock absorber for actuating the position device for the pressure roll and/or a guide plate for a strip coiler has a significant advantage over pneumatic systems alone in that it allows a reduction in the stress which may result from the interaction of the pressure roller and the periphery of the strip coil during the coiling operation and also results in a more rapid presetting of the pressing roll by reducing the distance of the latter from the strip coil periphery.
With the strictly pneumatic control, the response of the pressing roll or the guide varied depending on the displacement of the pneumatically actuated piston while, in the arrangement of the hydraulic shock absorber, the operating characteristics of the nitrogen accumulator depended directly upon the prevailing working pressure of the fluid medium feed to the hydraulic cylinder. The spring rate of the nitrogen accumulator was thus a function of the prevailing working pressure of the hydraulic fluid and could not be selected independently thereof.